Grinding wheel



Jan. 6, 1953 E. D. TEAGUE 2,624,660

GRINDING WHEEL Filed Sept. 7, 1950 Inverrfor ERNEST DUIJG'LAS TEAGL/E By ATTorrle] Patented Jan. 6, 1953 GRINDING WHEEL Ernest Douglas Teague, Welwyn Garden City,

England, assignor to Norton Company, Worcester, Mass., a corporation of Massachusetts Application September 7, 1950, Serial No. 183,552 In Great Britain September 29, 1949 4 Claims.

The invention relates to grinding wheels particularly to that variety thereof known as coping wheels, which are used to cut stone and other hard non-metallic materials.

One object of the invention is to provide a superior coping wheel. Another object of the invention is to provide a coping wheel which can be used in dry grinding operations and which will cut at a high rate without fracturing. Another object of the invention is to provide a coping wheel which can be used under conditions which will make it very hot without fracturing. Another object of the invention is to provide a coping wheel which can be used under such conditions that it becomes very hot and which nevertheless has a high rate of cut and relatively low wheel wear.

Other objects will be in part obvious or in part pointed out hereinafter.

In the accompanying drawings illustrating two of many possible embodiments of the mechanical features of this invention.

Figure 1 is a side elevation of a typical steel center for a coping wheel, the boundaries of the abrasive material to be molded thereon being indicated by dotted lines,

Figure 2 is a fragmentary diametral crosssectional View on a larger scale than Figure 1 of a coping wheel constructed in accordance with the invention,

Figure 3 is a cross-sectional view similar to Figure 2 illustrating another embodiment of the invention.

For the manufacture of a coping wheel in accordance with the invention, I provide a' steel center such as the steel center 10. This steel center ill as illustrated in Figure 1 is a typical shape of steel center for coping wheels, the shape in cross section of the peripheral portion being shown in Figures 2 and 3. This steel center Ill has cut-outs H at the periphery thereof forming a plurality of peripheral dovetails [2. Desirably also a plurality of holes l3 are provided in the peripheral portion i l in which the dovetails H are formed; this peripheral portion M is separated from the hub portion I5 by means of shoulders l6, one on each side of the center In. The hub portion It has a central hole I! so that the center In can be mounted upon a spindle. The sides of the hub portion l5 may be plane parallel surfaces and the sides of the peripheral portion I4 may also be plane parallel surfaces. The section planes of Figures 2 and 3 are not taken through the cut-outs H or holes l3. The foregoing description of the steel center it is illustrative and other shapes and styles of steel centers may be used in accordance with this invention. It will be seen that the steel center It is essentially a disc modified by the features above described.

On the steel center It is molded an annular portion 20 of abrasive and phenolic resin bond. This annular portion 20 is continuous around the entire steel center It and interlocks with the dovetails l2 and holes I 3. Between the steel center [0 and the annular portion 2% is a layer 25a of shellac as shown in Figure 2 or a layer Nb of shellac including granular, refractory or abrasive material, as shown in Figure 3.

The abrasive material in the annular portion 26 is preferably silicon carbide abrasive since this abrasive is preferred for the grinding of most stones such as granite, marble or the like, or the grinding of other hard non-metallic materials such as porcelain, glass and concrete. However, within the scope of the invention other abrasives may be used such as aluminum oxide abrasive including the product of the electric furnace or natural corundum or emery.

The bond in the annular portion 26 is a phenol formaldehyde resin of any desired variety. Commercial resins usually contain a minor proportion of cresol formaldehyde and such resins can be used advantageously in this invention. Furthermore I use the word phenol in the broad sense to include phenolic bodies such as cresol and xylenol. These, as well as phenol in the stricter sense, comprise a benzene ring with an OH group thereon. In making up the mixture furfural can be used as a plasticizer in which case there will result some furyl methylene linkages as well as methylene linkages. The uncured resin may have a substantial proportion of hexamethylenetetramine therein to speed the curing. In any case the resin bond should be cured to a thermo-irreversible condition. This resin bond I will term thermo-irreversible phenol-formaldehyde resin. This class of material and the manner of curing and compounding it is now well known in the abrasive art and also in other arts and therefore needs no further description. The proportions of the abrasive and of the thermo-irreversible phenol-formaldehyde resin, the grit size of the abrasive, the porosity of the annular portion 20 may all be varied within the usual limits and in accordance with the practices now well known in the abrasive art and particularly adapted for coping wheels. These matters, therefore, need no further elucidation herein.

The layer 21a consists of and the layer 2lb comprises shellac. Shellac is a natural resin and is well known so it needs no further definition.

In order to form the annular portion 20 with the layer Zia of shellac thereunder on the center ID, the following procedure may be adopted: the steel center I is thoroughly cleaned on both sides of the peripheral portion 14 and on both sides of the hub portion 15 near the shoulders ['5 to remove grease therefrom, and this may be done by immersing these portions in a suitable grease solvent such as gasoline. These portions are then coated with a solution of shellac. Any suitable solvent may be used, acetone, methyl alcohol and ethyl alcohol being examples. The shellac solution is then allowed to dry at room temperature and then another coating of the solution is applied. These steps are repeated until a layer of shellac of the required thickness is obtained. That is to say, the solution is brushed on, dried, more of the solution is brushed, dried again, still more of the solution is brushed on, dried again, and these steps are repeated over and over until the layer has been built up to the required thickness. This required thickness is not less than one thirty-second of an inch and may be varied in accordance with the grit size of the abrasive in the annular portion 20, being greater the greater the grit size. There is, however, no upper limit to the thickness of the layer Zia excepting that that part of the annular portion 26 outside of the layer 21a on either side should have a thickness at least as great as that of the layer 2% a within it. For shellac the best solvent is ethyl alcohol.

In order to form the annular portion 29 a suitable mold can be used. A layer of a mixture of uncured phenolformaldehyde resin and abrasive can be placed in the mold, then the center 10 with the layer 2 la can be placed thereon, then 4;

a further layer of resin and abrasive can be added and levelled off, the top plate of the mold can then be placed in position, the contents of the mold can then be pressed in an hydraulic press thereafter the center Ki with pressed layer Zia and pressed annular portion 25 can be stripped from the mold and cured in an oven. This technique of molding, pressing and curing grinding wheels including coping wheels is now well known in the art so it need not further be described herein. Also various ways of coinpounding a mixture of uncured resin and abrasive are well known and need not be further described. However it is pointed out that, just prior to inserting the center H) with the layer 2 Ia into the mold, the last brushing on of the solution of shellac should be done without any subsequent drying step as this promotes adhesion of the layer 2 la, to the annular portion The curing in an oven should be sufiicient that is to a high enough temperature and for a long enough time to convert the uncured phenol-formaldehyde resin to the thermo-irreversible stage, the temperatures and times necessary to do this being also well known. During this curing the remainder of any solvent in the shellac is driven 01f and the layer 21a becomes rigid and adheres firmly to the center [0 but it is still slightly plastic when heated.

For the formation of the annular portion 29 with the layer 2Ib of shellac thereunder on the center I0 I may proceed as above with the following differences: a first coating of the solution of shellac is applied and dried at room temperature. Abrasive grain, refractory grain or '4 other inert (at the temperatures involved) granular material is coated with the shellac and this can be done by mixing the granular material with a solution of shellac and subsequently drying to evaporate the solvent, and these steps may be repeated several times to build up a substantial layer of the shellac on each granule, three repeats of the coating process being suflicient and even one such coating being adequate in many cases. The granular material can be ordinary sand such as quartz sand, or abrasive such as aluminum oxide abrasive or silicon carbide abrasive can be used. The grit size of this granular material can be varied but ordinarily should not be greater than the grit size of the abrasive in the annular portion 20; I have had good results using granular material of mesh grit size for this purpose. If the granules of the granular material stick together screening or other procedure should be employed to separate the individual granules at least for the most part. The granular, refractory or abrasive material in the layer 21b may be properly described generically as inert material. It functions as an inert filler.

Now the steel center is brushed a second time with the solution of shellac and while the coating thus produced is still in a tacky condition the center is rolledin the coated granular material above described. Then, if the thickness of the coating is not yet sufficient, the coating is air dried. Application of solution, rolling and air drying is then continued or repeated until the desired thickness of coating has been attained, but as in the previous case the last applied portion of the coating is not permitted to air dry but rather the molding operation previously described is undertaken while the coating which now constitutes the layer 2H2 is still in a tacky condition. The rest of the procedure is or may be as above described. The thickness of the layer 212) should also be not less than one thirty-second of an inch and may be varied in accordance with the grit size of the abrasive in the annular portion 20, being greater the greater the grit size, and there is likewise no upper limit to the thickness of the layer 2| 1) excepting as stated in connection with the layer 21a.

The excellence of thermo-irreversible phenolformaldehyde resin as a bond for the manufacture of coping Wheels is already known. That is to say coping wheels having the abrasive portion bonded with thermo-irreversible phenol-formaldehyde resin give superior results when measured by proper standards to coping wheels the abrasive portion of which is bonded with any other organic bond now known. However the abrasive portion, when bonded with thermo-irreversible phenolformaldehyde resin, has frequently fractured especially when the coping wheels have been used in dry grinding. Dry grinding operations heat the abrasive portion and in so much as the steel center may be relatively cool, being a good conductor of heat, and furthermore since the coefiicient of thermal-expansion of the abrasive portion and the steel center is different, break-ages have been frequent. The present invention, however, solves this difficulty in that the plasticity of the layers 25a and 2!?) is such as substantially to eliminate this cause of Wheel breakage. Expansion of the annular portion 28 relative to the steel center I0 is accommodated by the layer 2 I a or the layer 2 lb which, especially when heated, will deform, stretch or bend instead of breaking. Furthermore I have found that the adhesion of the layers 2| a and 2 lb to the steel center [0 and to the portion 5 20 is entirely satisfactory. Thus the invention provides a coping wheel which is highly efficient in operation, can be used in dry grinding operations, and will not readily fracture.

I have illustrated and described two practical embodiments of the invention. I now prefer the embodiment shown in Figure 3 Where the layer 2 lb underlies the abrasive portion 20. This is for the reason that the layer 2 lb is a little stronger than the layer 2 la. However for many wheels the layer 21a is adequate and it is a little simpler to make a wheel having the layer '2 la than it is to make a wheel having the layer 211).

It will thus be seen that there has been provided by this invention a grinding wheel particularly of that variety known as a coping wheel in which the various objects hereina'bove set forth together with many thoroughly practical advantages are successfully achieved. As many possible embodiments may be made of the above invention and as many changes might be made in the embodiments above set forth, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. A coping whee1 comprising a steel center, an annular abrasive portion of abrasive grain bonded with theme-irreversible phenol-formaldehyde resin on the periphery of said steel center, and a layer of shellac between said abrasive portion and said steel center on both sides of said steel center,

said layer being at least one thirty-second of an inch thick and said annular abrasive portion outside of the layer of shellac on both sides having a thickness at least as great as that of the layer of shellac within it.

2. A coping wheel as claimed in claim 1 in which the layer of shellac includes particles of inert material.

3. A coping wheel comprising a steel center, an annular abrasive portion of abrasive grain bonded with thermo-irrev-ersible phenol-formaldehyde resin at least one thirty-second of an inch thick on the periphery of said steel center, and a layer of shellac between said abrasive portion and said steel center on both sides of said steel center, said layer being at least one thirty-second of an inch thick and said annular abrasive portion outside of the layer of shellac on both sides having a thickness at least as great as that of the layer of shellac within it. i

4. A coping wheel as claimed in claim 3 in which the layer of shell-ac includes particles of inert material.

ERNEST DOUGLAS TEAGUE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Kuzmick Jan. 6, 1942 Number 

1. A COPING WHEEL COMPRISING A STEEL CENTER, AN ANNULAR ABRASIVE PORTION OF ABRASIVE GRAIN BONDED WITH THERMO-IRREVERSIBLE PHENOL-FORMALDEHYDE RESIN ON THE PERIPHERY OF SAID STEEL CENTER, AND A LAYER OF SHELLAC BETWEEN SAID ABRASIVE PORTION AND SAID STEEL CENTER ON BOTH SIDES OF SAID STEEL CENTER, SAID LAYER BEING AT LEAST ONE THIRTY-SECOND OF AN INCH THICK AND SAID ANNULAR ABRASIVE PORTION OUTSIDE OF THE LAYER OF SHELLAC ON BOTH SIDES HAVING A THICKNESS AT LEAST AS GREAT AS THAT OF THE LAYER OF SHELLAC WITHIN IT. 